A dual rail power supply system is an apparatus for supplying two output voltages. A dual rail power supply system may comprise a positive voltage rail and a negative voltage rail, where the voltage provided at the negative voltage may be equal to the negative of the voltage provided at the positive voltage rail.
FIG. 1 is a schematic of a multi-phase dual rail power supply system 100. The power supply system 100 comprises a positive voltage rail 102 at an output voltage VO1 and a negative voltage rail 104 at an output voltage VO2. The output voltage VO2 in the present example is equal to the negative of the output voltage VO1. Other examples of multi-phase dual rail power supply systems may have an output voltage VO2 that is unequal to the negative of the output voltage VO1. The power supply system 100 comprises a multi-phase boost converter 106 and a multi-phase inverter converter 108. Also shown is a load 110 that draws a load current I_LOAD from the power supply system 100. The load 110 is represented by a current source and is coupled between the voltage rails 102, 104.
The multi-phase boost converter 106 comprises two boost converters 106a, 106b and the multi-phase inverter converter 108 comprises two inverters 108a, 108b. The boost converter 106a comprises an inductor 112, two switches 114, 116 and a capacitor 118. The boost converter 106b comprises an inductor 120, two switches 122, 124 and a capacitor 126. The inverter 108a comprises an inductor 128, two switches 130, 132 and a capacitor 134. The inverter 108b comprises an inductor 136, two switches 138, 140 and a capacitor 142. Inputs of the boost converter 106a and the inverter 108a are coupled to a voltage supply 144 providing an input voltage VIN and a first terminal of a capacitor 146 with a second terminal coupled to ground. Inputs of the boost converter 106b and the inverter 108b are coupled to the voltage supply 144.
Dual rail power supply systems may be single phase or dual phase. A single phase dual rail power supply system may, for example, comprise a single boost converter (comprising an inductor) and a single inverter (comprising another inductor) configured to provide the two output voltages. A single phase dual rail power supply system only requires a single power stage to provide energy. Due to the saturation current of the inductors included in single phase systems they are typically not able to provide a sufficiently high output current to support the load current requirements of many modern electronic systems. This problem was overcome by the introduction of multi-phase systems, such as the power supply system 100, that can support high current positive voltage rail and negative voltage rail applications that require higher load currents. Compared to a single-phase system, a multi-phase power supply system can be used to increase the output current capability in high output current demand systems.
However, a drawback is that a multi-phase system needs more inductors than a single phase system; four inductors are required to realize high output current capability via multi-phase control, as shown in FIG. 1. Furthermore, the multi-phase system requires greater printed circuit board (PCB) area and more components (for example passive components). This means the cost is higher when compared to a single-phase system and the circuitry becomes more complex due to more phases and the requirement for an additional current balance control circuit.